1. Field of the Invention
The present invention relates to simulated stone products and to the method of making them. More particularly, the invention relates to simulated stone building components used for architectural detail in residential and commercial buildings.
2. Description of the Prior Art
Historically, carved limestone has been a preferred material for window surrounds, fireplaces and other decorative features, for use with brick or natural stone on expensive, estate-type residences. It has also been used extensively on many institutional and class "A" office buildings. However, carved limestone is heavy and difficult to handle by workmen, and depending upon the size may require the use of machinery to lift it. In addition, in more recent times carved limestone and other stone carvings have become prohibitively expensive and have been dropped from general use in the second half of this century.
There is a long history of the search for a material which provides the look of traditional carved stone at a more economical cost, and many substitute materials have been developed with varying degrees of success. Examples of some prior art attempts are disclosed in U.S. Pat No. 4,346,050(Trent), U.S. Pat. No. 4,473,673(Williams), U.S. Pat. No. 5,275,582(Jones),U.S. Pat. No. 5,422,391(Inoue) and U.S. Pat. No. 5,478,390(Cruaud).
The Trent patent is directed to an improved concrete product having a very low viscosity (no more than about 50 centipoise) polyester resin binder so that the concrete will have higher strength and other improved properties such as high modulus of elasticity, low thermal expansion and contraction, better fire resistance and low shrinkage on curing. The improved concrete product disclosed in this patent is intended for use in the production of pre-cast elements for architectural or engineering applications in building construction. In order to achieve different surface appearances for various architectural uses, the surface of the concrete product described in this patent can be treated or etched with any solvent for the polymer binder so that an exposed aggregate effect is obtained.
The Williams patent is concerned with the production of a simulated or cultured marble product, and mixes an unsaturated polyester resin having a viscosity of about 300-600 centipoise (CPI) with a solid filler material such as calcium carbonate and then subjects the composition to a three step process, i.e., evacuating, vibrating and shearing under carefully controlled and limited conditions. The resulting product has a smooth, glossy surface finish and is particularly suitable for use in making countertops, bathroom sinks, table tops, lamps, etc.
The Jones patent is concerned with a simulated stone product for use as a basic building component and uses a resin binder with sodium chloride particles, pigments and other fillers to yield desired aesthetic effects. The mixture is cast in a mold that has been coated with a gel coat to produce countertops, sinks, tubs, etc. The resulting product has a glossy surface finish, and because of the use of sodium chloride has a high degree of whiteness.
The patent to Inoue describes a method of making a high density artificial stone having physical properties similar to those of natural stone, e.g., marble. In producing his product, Inoue molds a mixture of natural stone particles with calcium carbonate filler and a resin binder. Various colors may be given to the finished product by using colored particulate materials, or introducing pigments. The surface of the cast product is processed with an organic solvent to remove resins. Alternatively, the surface may be given an uneven texture by scraping the surface with a wire brush or the like, or spraying it with a high pressure water jet.
The patent to Cruaud relates to a process of making cuttable concrete having hardness and other properties permitting its use in ways that conventional concrete may be used, but having the additional property of being cuttable with conventional sculpting tools. After it is cast, the concrete product may be sandblasted to imitate the external appearance of a natural stone.
Although many of the prior art efforts have successfully attained the architectural shapes desired, none of them have produced an inexpensive cast product for simulating stone as an architectural feature in a building, wherein the casting is lightweight and durable in construction, with improved density and a surface texture which gives the desired appearance of high quality carved stone.
Because of the difficulty of producing a simulated stone product having the properties described above, cementitious concrete castings are the standards of the present day synthetic stone industry. The most popular casting methods are dry cast (Cast Stone) and wet cast (Pre-cast Concrete). Dry cast masonry materials (Cast Stone) more closely imitate a stone surface than any of the readily available substitutes. However, there are serious limitations with these products. Cast Stone is weak in tensile strength and is very porous. It can not be economically cast in complex shapes requiring curved surfaces or sharp arises. When complex shapes are achieved, the resulting castings are easily chipped. Cast Stone, like all other cementitious castings, are bulky and heavy. Moreover, larger castings must be steel reinforced. It is also susceptible to cracking and deterioration due to the freeze-thaw cycle experienced in northern climates.
In wet cast cementitious concrete, the look of stone is achieved by exposing the aggregate in the casting by chemically or mechanically removing the cement paste from the surface after the casting has hardened. When a large aggregate is used (3/4 inch or larger) the process results in a stone-like appearance when viewed from a distance, but when viewed close up the casting is not the equivalent in appearance of carved stone. For instance, when cementitious concrete castings use a smaller aggregate (sand) they can achieve a closer similarity to carved stone, but the smaller aggregate makes the surface weaker and more porous and causes the casting to lose detail. In addition, because of the nature and strength of cementitious concrete, the castings are thick and heavy and fine detail can not be achieved.
Further, chemical or mechanical exposure of the aggregates leads to other problems, i.e., when chemical means are employed, satisfactory results occur on large aggregate castings, but surface imperfections occur when a small aggregate material such as sand is used. When mechanical means, e.g., sand blasting, is employed, surface imperfections such as air pockets are opened up on large aggregate castings and the surface appearance rapidly deteriorates. The smaller the aggregate, the more acute the problem. Therefore, fine stonelike finishes in wet cast cementitious concrete is a virtual impossibility.
In the past, applicant experienced difficulties when using resin binders in combination with various aggregate materials in an effort to solve the problems of prior art techniques. For instance, a surface retarder can not be used with polyester resin binders during the casting process as is common with cementitious concrete castings. Previously, applicant used a chemical which broke down the polyester binder on the surface of the casting and then removed the chemical with soap and water. This resulted in a casting with a satisfactory look of carved stone because any air bubbles on the surface or just below the surface were filled with a mixture of fine aggregate and broken down resin which filled any surface imperfections during the stripping process. However, this process required the use of toxic and hazardous materials and was therefore uneconomical because of the environmental hazards of such materials and the increased costs associated with use of them. Applicant therefore sought to develop a more economical method of achieving a stone-like surface by using sandblasting. Although sandblasting is a very economical method of finishing a casting, the primary impediment to use of sandblasting as a finishing method is the presence of small air bubbles near the surface which open up and cause unsightly surface imperfections when the resin skim coat is removed.
Further, building components used for architectural detail such as door and window surrounds are typically manufactured in a desired shape and installed around the window and door openings prior to the time a brick mason or stone mason constructs the brick or stone facing of the building. Conventional window and door surrounds do not make any special provision for the brick or stone facing to be later applied. Consequently, the brick mason or stone mason must cut or notch the bricks or stones to accommodate the shape of the previously installed door and/or window surrounds, adding to the difficulty and cost of applying the brick or stone facing.
Accordingly, there is need for an economical, lightweight simulated stone product for use in the building industry, and especially wherein the simulated stone product is strong and durable and accurately simulates the appearance of high quality cut stone. Further, there is need for a building component for use in providing architectural detail to a building, e.g., window and door surrounds, which has provision for accommodating bricks or stones subsequently installed by a masonry worker, without the need for cutting or shaping the bricks or stones to accommodate the shape of the architectural detail building component.